Electric meter including pivoted mag-
net rotor surrounded by continuous
pole faces



3,2 75,936 UNDED BY P 27, 1966 w. D HUSTON ELECTRIC METER INCLUDINGPIVOTED MAGNET ROTOR SURRO CQNTINUOUS POLE FACES Flled May 4, 1962INVENTOR. WILLIAM D. HUSTON Patented Sept. 27, 1966 3,275,936 ELECTRICMETER INCLUDING PIVOTED MAG- NET ROTOR SURROUNDED BY CONTINUOUS POLEFACES William D. Huston, Rochester, N.Y., assignor to American Radiator& Standard Sanitary Corporation, New York, N.Y., a corporation ofDelaware Filed May 4, 1962, Ser. No. 192,452 3 Claims. '(Cl. 324146) Thepresent invention relates to voltmeters, and has to do primarily with avoltmeter of the general type having a coil mounted on a fixed armature,and a rotor including a permanent magnet.

Voltmeters of this type are inexpensive and rugged. Heretofore, however,they have been subject to relatively severe limitations with regard totheir accuracy and sensitivity, because of the inherent tendency of thepermanent magnet to align itself with the armature due to its ownmagnetic field. Because of this effect, it has heretofore been thoughtnecessary in voltmeters of this general type to provide a relativelylarge spacing between the rotor permanent magnet and the pole faces ofthe armature, thus leaving a relatively large gap in the magneticcircuit of the armature. This construction makes for relatively highreluctance in the armature circuit; and previous meters of this type,therefore, have been characterized by a lack of sensitivity.

Accordingly, one important object of the present invention is to improvethe sensitivity of voltmeters of this type without sacrifice ofaccuracy, reliability and other desirable characteristics.

Another object is to provide a voltmeter of the stated type in which thepivoted permanent magnet may be closely spaced from the pole faces ofthe armature without developing an angular bias on the magnet due to itsown magnetic field.

Another object is to provide a voltmeter of the stated type which may beeasily and quickly calibrated, thereby facilitating production.

A general object of the invention is to provide a voltmeter of thestated type which is relatively inexpensive to manufacture, compact,requires a minimum number of parts, yet is rugged and of long-lastingconstruction, and is well suited for mass production by relativelyunskilled personnellar aperture in the armature, within which thepermanent magnet rotor is pivoted for rotation in response to magneticflux developed in the armature by current passing through the coil. Bymaking the gap in the form of a circular aperture centered on the pivotaxis of the rotor, the rotor is made insensitive to the relativeorientation of the armature, and no torque is produced on the rotor dueto the interaction of the magnetic field of the rotor magnet and thearmature. The spacing between the poles of the pivoted permanent magnetand the armature is the same for all angular positions of the armature.

In the illustrated embodiment, a biasing, or restoring magnet is fixedrelative to the armature adjacent to the rotor for urging the rotortoward a selected zero indicating position.

The meter movement forms a sub-assembly, which may be quickly and easilycalibrated prior to mounting in the meter case, by simply bending oneleg of the armature toward or away from the opposite leg. This actionadjusts the reluctance of the magnetic circuit, and thereby adjusts thesensitivity of the movement by varying the magnitude of the fluxproduced in the armature in response to a given applied voltage.

Referring now to the drawing by numerals of reference, the voltmetershown includes a cup-like case 10, preferably made of a magneticmaterial such as sheet steel so that it will shield the meter movementfrom external magnetic fields. The open end of the case 10 is coveredbya crystal 12, which is held in place by a conventional bezel 14 and aspacer ring .16. A graduated dial 18 is held in position near the openend of the easing .10 between the spacer ring 16 and inwardly extendingbosses 20, which are struck from the sidewall of the case 10 at spacedpoints therearound.

The meter movement 22 is mounted within the case 10 mostly behind thedial 18, and includes a pointer 24, which extends through an aperture 26in the dial 18,

' land which is arranged to swing across the dial to indicate the valueof the voltage being measured. The movement 22 is secured by a grommet32 to an insulating plate 28, which extends across the back wall of thecase 10 and is angularly fixed relative thereto by engage- The foregoingand other objects and advantages of the j invention will become apparentfrom the following detailed description of a representative embodimentthereof, taken in conjunction with the drawing, wherein:

FIG. 1 is a front elevational view of a voltmeter made according to thepresently preferred embodiment of the invention;

FIG. 2 is a plan view of this voltmeter;

FIG. 3 is a front elevational view, on an enlarged scale but with partsbroken away, of this voltmeter, showing the arrangement of the internalparts thereof; and

FIG. 4 is a cross-sectional view of this voltmeter.

The voltmeter of the present invention, like previous voltmeters of thetype having pivoted permanent magnet rotors, is of rugged construction,especially adapted for use on motor vehicles where relatively severevibration and shock may be encountered. The voltmeter of the invention,however, has improved accuracy and sensitivity. It includes a magneticarmature, which mounts an energizing coil to which the voltage to bemeasured is applied. The magnetic gap is preferably formed by acircument with diametrically opposed bosses 30 struck inwardly from theside wall of the case 10.

The movement 22 includes an armature or core 34 made of .a paramagneticmaterial such as a silicon steel alloy having relatively low reluctanceand low coercive force. The armature or core 34 is in the form of arelatively thin ribbon bent in a U-shape, and is secured to theinsulator plate 28 by the grommet 32, which extends through both legs 38and 40 of the armature, and which is of a non-magnetic material such asbras-s. A spacer bushing 36 is fitted around the grommet 32 between thefront leg 38 of the armature and the insulating plate 28 to maintain thedesired spacing between the two legs 38 and 40 of the armature. Thebushing 36 is also of a non-magnetic material such as brass. The backleg 40 of the armature or core passe-s behind the insulating plate 28and rests against an inwardly-protruding central boss on the back wallof the case 10. The energizing coil 42 is mounted on the front leg 38 ofthe armature or core, and is retained thereon between the grommet 32 anda pair of laterally extending shoulders 44 on the armature.

There is a circular aperture 50 in the front leg 38 of the armature orcore 34 near the bight portion thereof,

constituting a gap in the low reluctance flux path of the armature orcore. A rotor 46 is pivoted within the aperture 50 for rotation inresponse to a magnetic flux developed in the armature or core. The rotor46 is pivoted on a stem 48 staked to the rear leg 40 of the armature orcore in axial alignment with the aperture 50. The stem 48 includes aflange 52 for engagement by a nonmagnetic retainer cup 54, which fitswithin the aperture 50 in the front leg of the armature-or core, andwhich serves the dual purposes of maintaining the stem 48 in coaxialalignment with the aperture 50 and of retaining a restoring magnet 56upon the ,stem. The restoring magnet 56 is annular in form, and isfitted around the stem 48 between the retaining cup 54 and the rear leg40 of the armature or core. The restoring magnet 56 is magnetized in adirection parallel to the plane of rotation of the rotor 46 and at about45 from the direction of the length of the armature or core 34. Therotor 46 includes a hub or bushing 58, which fits upon the stem 48 andis freely rotatable thereon, and a permanent magnet 60 of generally ovalshape, which is staked, or otherwise fixed on the hub or bushing 58along with the pointer 24. The rotor magnet 60 is magnetized in adirection parallel to its plane of rotation and approximately normal tothe length of the pointer 24.

The movement 22, including the insulating plate 28 constitutes asub-assembly, and is secured in the case by a pair of studs 62 and 64,which extend through the insulating plate 28 and through the back wallof the case 10. The studs 62 and 64 are electrically insulated from thecase by appropriate insulating bushings and washers (not separatelydesignated). The coil 42 is connected to the studs 62 and 64 by terminalrings 66 and 68, which are positioned between the heads of the studs 62and 64 and the insulating plate 28. A resistor 70 is connected in serieswith the coil 42 between the ring 66 and the coil for limiting thecurrent in the coil 42. The value of the resistor 70 is selected inaccordance with well known principles in view of the magnitude of thevoltage it is desired to measure with the voltmeter.

In operation, the restoring, or biasing magnet 56 urges the rotor 46 andthe pointer 24 toward zero indicating position by reason of the magneticattraction between the restoring magnet 56 and the rotor magnet 60'. Therotor magnet 60 tends to align itself with the restoring magnet. Whencurrent passes through the coil 42 in response to a voltage appliedbetween the studs 62 and 64, a magnetic flux is established in thearmature or core 34, and rotates the rotor 46 in proportion to themagnitude of the current. This flux tends to urge the rotor 46 in aclockwise direction as viewed in FIGS. 1 and 3. The manner in which theflux operates to rotate magnet 69 is not fully understood; but it issurmised that the narrow areas at opposite sides of the aperture 50 in adirection transverse of the armature or core tend to constrict theelectrically induced flux, thus producing a saturated condition. Theflux is, therefore, directed through rotor 60 as the easiest path. Therestoring magnet 56 is oriented, and the direction of current flow inthe coil 42 is chosen so that the rotor '46 is driven across the 135angle between the restoring magnet 56 and the armature or core 34 ratherthan the complementary 45 angle. Full scale deflection may include anangle of 90, or more, without encountering severe variations from alinear response relative to the current passing through, and of thevoltage applied across the coil 42. When the voltage is removed, themagnetic flux in the armature or core 34 ceases, and the restoringmagnet 56 draws the rotor 46 back to its zero indicating position.

With the magnet 60 positioned in the center of the circular aperture 50,the magnet is not influenced by the soft iron armature or core 34 in anydirection until coil .42 is energized. The soft iron armature or coreinsures that the magnetic flux will be concentrated in one direction, torotate the magnet 60. The magnet 60 can be of a length approximatelyequal to the diameter of the aperture 50; only mechanical clearance isrequired between the aperture and the rotor magnet 60. The armature orcore 34 extends completely around the rotor magnet 60, and the aperture50 is circular so that the forces produced between the permanent magnet60 and the armature or core 34 by the permanent magnet 60 areindependent of the angular position of the magnet 60 and do not includean angular component for any position of the rotor 46.

The magnet 56 serves not only as a return magnet but also to retain therotor 46 on the stem 48. No other retaining device is included. The dial18, however, extends over the rotor 46 and serves as an abutment stop tokeep the rotor 46 from escaping from the stem 48 in the event ofexceptionally severe shocks.

A mounting clamp, or strap 72 is carried by the studs 62 and 64 for easymounting of the meter on the instrument panel of a vehicle, or the like.The clamp 72 is insulated from the studs 62 and 64 by appropriateinsulating bushings and washers (not separately designated). When themeter is to be used in a vehicle wherein one of the battery terminals isgrounded, a shorting cup 74 is provided on one of the studs 62 and 64for grounding the corresponding terminal of the meter to the mountingbracket 72.

In manufacture, preliminarily to mounting the movement 22 in the case10, the movement 22 is calibrated by applying a voltage of knownmagnitude to it, and then bending the upper, free end of the rear leg 40of the armature toward or away from the front leg 36 until the properdeflection of the pointer 24 is noted. Bending the rear leg 40 towardthe front leg 38 reduces the overall reluctance of the magnetic circuitof the armature 34, thereby increasing the flux produced in response toa given voltage,-and increasing the meter reading. Bending the rear leg40 away from the front leg 36 increases the reluctance, reduces theflux, and reduces the reading.

While the invention has been described in connection with a specificembodiment thereof, it will be understood that it is capable of furthermodification, and this application is intended to cover any variations,uses, or adaptations of the invention following, in general, theprinciples of the invention and including such departures from thepresent disclosure as come within known or customary practice in the artto which the invention pertains and as may be applied to the essentialfeatures hereinbefore set forth, and as fall within the scope of theinvention or the limits of the appended claims.

Having thus described my invention, what I claim is:

1. An electrical meter comprising (a) a generally U-shaped corecomprising a single sheet of thin, soft magnetic material,

(b) an electric coil mounted on one leg of said core for producingmagnetic flux therein upon energization of said coil,

(c) said core having a circular aperture in one leg with a continuouscircular wall, said aperture extending across the major part of thewidth of the core whereby two magnetically saturable portions of thecore are disposed at either side of the aperture,

(d) a permanent magnet, means pivoting said permanent magnet in saidaperture, said magnet being polarized in the plane of said aperture, and

(e) means for biasing said magnet toward -a preselected angular positionrelative to said core, and means for adjusting the reluctance of saidcore for calibrating said meter. 2. An electrical meter as claimed inclaim 1, wherein, for the purpose of calibrating said meter, one leg ofsaid core is bendable toward and away from the opposite leg thereof. 3.An electrical meter as claimed in claim 1, wherein said biasing means isan annular magnet coaxial with 5 said pivoting means, and said permanentmagnet is ro- 2,411,997 tatable about the axis of said pivot. 2,498,7262,867,768 References Cited by the Examiner 2 3 9 520 UNITED STATESPATENTS 5 1,985,082 12/1934 Fans 324-151 2,040,060 5/1936 Middleton324140 Kelly 324-146 Towner 324-146 X Fribance 324-446 Chapman 324146WALTER L. CARLSON, Primary Examiner.

R. V. ROLINEC, Assistant Examiner.

1. AN ELECTRICAL METER-COMPRISING (A) A GENERALLY U-SHAPED CORECOMPRISING A SINGLE SHEET OF THIN, SOFT MAGNETIC MATERIAL, (B) ANELECTRIC COIL MOUNTED ON ONE LEG OF SAID CORE FOR PRODUCING MAGNETICFLUX THEREIN UPON ENERGIZATION OF SAID COIL, (C) SAID CORE HAVING ACIRCULAR APERTURE IN ONE LEG WITH A CONTINUOUS CIRCULAR WALL, SAIDAPERTURE EXTENDING ACROSS THE MAJOR PART OF THE WIDTH OF THE COREWHEREBY TWO MAGNETICALLY SATURABLE PORTIONS OF THE CORE ARE DISPOSED ATEITHER SIDE OF THE APERTURE, (D) A PERMANENT MAGNET, MEANS PIVOTING SAIDPERMANENT MAGNET IN SAID APERTURE, SAID MAGNET BEING POLARIZED IN THEPLANE OF SAID APERTURE, AND (E) MEANS FOR BIASING SAID MAGNET TOWARD APRESELECTED ANGULAR POSITION RELATIVE TO SAID CORE, AND MEANS FORADJUSTING THE RELUCTANCE OF SAID CORE FOR CALIBRATING SAID METER.